The present invention relates to a method for production of a solid oxide fuel cell (SOFC) having an electrolyte body in tubular form, wherein at least one internal electrode and one external electrode are applied to the electrolyte body.
Solid oxide fuel cells (SOFC) with a ceramic electrolyte body form a high-temperature variant of fuel cells. They are operated at 600° C. to 1000° C., and in the process provide very high electrical efficiencies of up to about 50%. In principle, solid oxide fuel cells are subdivided into two main variants: one variant is formed by a tubular shape of the electrolyte body which, according to a further variant, can be bounded, by a flat, planar form. In this case, it is necessary to fit the internal and external electrodes to the wall of the electrolyte body during the method for production of a solid oxide fuel cell based on the tubular variant. For this purpose, it is known for the electrode which is arranged on the inside of the electrolyte body, generally in the form of the anode, around which the fuel gas flows, to be applied as a coating on the inner wall of the electrolyte body. In this case, the electrolyte body is preferably extruded.
In addition to the mounting of the electrodes on the finished electrolyte body, so-called interconnectors are applied flat to the electrodes in order to make contact with them, in which case fitting on the inside of the electrolyte body frequently leads to problems. Metallic interconnectors are known, which are composed of a material with a high chromium content, in order to obtain adequate corrosion resistance, combined with adequate electrical conductivity, on the basis of the high operating temperatures. The chromium-oxide layer which is formed during operation of the fuel cell in this case has a negative effect on the cathode material, and can lead to premature aging of the fuel cell. In contrast, ceramic interconnectors for making electrical contact with the electrodes are known in the planar form, but have not previously been used for tubular solid oxide fuel cells. Because the electrolyte bodies are very thin, there are major problems associated with fitting ceramic interconnectors to the inner wall of the electrolyte body. The problem results in particular from the thin walls since, for example, the electrolyte body preferably has a wall thickness of about 200 μm, in which case the porous anode on the inside of the electrolyte body must be coated with a ceramic interconnector layer. For cost reasons, the electrodes themselves must likewise be made thin, for example with a thickness of 50 μm. Furthermore, the interconnector layer must likewise be highly porous, with further advantages being obtained from the interconnector material on the surface of the electrolyte body having a thickness which varies over the longitudinal extent of the electrolyte body.